In a wireless communication or radar system, a device for receiving wireless signals is generally referred to as a wireless receiver or receiver. There exist numerous types of receivers, and a major index of the receiver used for evaluating the performance of the receivers is the dynamic range.
The dynamic range of a receiver includes a simultaneous dynamic range and a non-simultaneous dynamic range. The simultaneous dynamic range refers to a capability of the receiver of demodulating a large signal and a small signal simultaneously and accurately in the case where the large signal and the small signal coexist, and a value of the simultaneous dynamic range is generally the maximum value of a ratio of the power of the large signal to that of the small signal. The non-simultaneous dynamic range refers to a capability of the receiver of demodulating a fluctuant signal which varies with the time, and a value of the non-simultaneous dynamic range is generally a ratio of the maximum power of the fluctuant signal to the minimum power of the fluctuant signal. If a large signal and a small signal inputted simultaneously to the receiver can be demodulated accurately by the receiver, the large signal and the small signal can certainly be demodulated accurately by the receiver when the large signal and the small signal are inputted non-simultaneously because no interference exists between the large signal and the small signal. Therefore, the non-simultaneous dynamic range of a receiver is typically larger than the simultaneous dynamic range of the receiver. In practice, the non-simultaneous dynamic range of the receiver can be extended using the Analog Automatic Gain Control (AAGC) technology.
At present, the AAGC technology includes a single variable-gain branch technology and a multi-fixed-gain-branch technology. In the single variable-gain branch technology, a single branch with variable gain is used to process the received signal. In the multi-fixed-gain-branch technology, multiple fixed-gain branches, each of which has a different fixed gain, are used to process the received signal.
FIG. 1 is a diagram showing the basic structure of a receiver receiving wireless signals using the single variable-gain branch technology. As shown in FIG. 1, the receiver with single variable-gain branch includes an upstream analog receiving path module, a variable-gain analog receiving path, an Analog-to-Digital Converter (ADC), a power detecting and AAGC control module, and a digital receiving path module.
The upstream analog receiving path module, which includes a low noise amplifier and may further include a frequency mixer, a filter, etc., preprocesses the received input signal. The input signal of the upstream analog receiving path module, i.e. the input signal of the receiver, is an analog band-pass signal. If the upstream analog receiving path module does not include analog I&Q demodulating components, the output of the upstream analog receiving path module is generally an analog band-pass signal; and if the upstream analog receiving path module includes analog I&Q demodulating components, the output of the upstream analog receiving path module are analog I&Q signals.
The variable-gain analog receiving path module includes multiple stages of frequency mixing, filtering, an amplification, etc., and the gain of the variable-gain analog receiving path module can be changed under the control of the power detecting and AAGC control module.
The ADC converts an analog signal to a digital signal. The ADC is a single-path ADC in the case where a single analog band-pass signal is inputted, and is a dual-path ADC, i.e. I&Q ADCs, in the case where analog I&Q signals are inputted.
The power detecting and AAGC control module processes the signal outputted from the ADC module to obtain a signal power value, determines gain configuration according to the signal power value, and changes the gain of the variable-gain analog receiving path under the control of a demodulation synchronization signal.
The digital receiving path module filters and decimates the signal outputted from the ADC to obtain a baseband signal, and demodulates the baseband signal to obtain a bit stream. A single bit stream is outputted by the digital receiving path module if the receiver is single-carrier receiver, and multiple bit streams are outputted if the receiver is a multi-carrier receiver.
As shown in FIG. 1, the variable-gain analog receiving path, the ADC and the power detecting and AAGC control module form a feedback loop. After the input signal passes through the upstream analog receiving path module, the variable-gain analog receiving path and the ADC, the power detecting and AAGC control module detects the power of the input signal, and sets the gain of the variable-gain analog receiving path to an appropriate value, according to the dynamic range of the receiver and a certain AAGC algorithm.
The single variable-gain branch technology is disadvantageous in the following aspects.
(1) Because power of the input signal is controlled using a feedback loop, it takes some time to update a gain of the receiver in response to a change of the input signal, so that the control speed is restricted by the response time.
(2) The power detecting and AAGC control module updates the gain under the control of a demodulation synchronization signal, not at an arbitrary point of time. In other words, the power detecting and AAGC control module can update the gain at synchronous boundaries only; otherwise, the change on the analog device gain and an induced phase change may impact the demodulation performance. Therefore, the gain of the receiver needs to be maintained constant within duration of the signal. In other words, a synchronous AAGC is required, as a result, circuitry complexity is increased and the channel change cannot be traced rapidly.
(3) If a large change on the input signal occurs within the duration of the signal and exceeds the non-simultaneous dynamic range of the single path, the signal passing through the variable-gain analog receiving path is inevitably saturated or lower than the sensitivity, regardless of the control by the AAGC. This results in an increased error bit rate.
In the prior art, the multi-fixed-gain-branch technology, as another AAGC technology, is characterized in that no feedback loop is required to control the gain; instead, multiple branches each having a different fixed gain are deployed to amplify the input signal, and a proper branch is selected to output. In other words, a switching between the branches is performed. A receiver built according to the multi-fixed-gain-branch technology generally includes a multi-fixed-gain-branch receiver which switches before demodulation and a multi-fixed-gain-branch receiver which switches after demodulation.
FIG. 2 is a diagram showing the basic structure of a multi-fixed-gain-branch receiver which switches before demodulation. As shown in FIG. 2, the receiver includes an upstream analog receiving path module, M fixed-gain branch modules, M ADCs, M digital receiving path fore-stages, a multi-branch synchronous switching module, and a digital receiving path post-stage.
The upstream analog receiving path module is the same as that of the single variable-gain branch receiver, and description thereof is omitted.
Compared with the single variable-gain branch receiver, the fixed-gain branch module also includes multiple stages of a frequency mixer module, a filter module, and an amplifier module, but has a fixed gain. Furthermore, gains of the M fixed-gain branch modules form a ladder distribution, which is referred to as ladder gain processing. For example, the gain of the first branch is 80 db, the gain of the second gain branch is 60 db, and the gain of the third branch is 40 db, and so on. In practice, the gain difference between two adjacent branches may be different.
Each of the ADCs is the same as that of the single variable-gain branch receiver, and description thereof is omitted.
The digital receiving path module performs processing, such as filtering and decimation, on the signal from the ADC for multiple times to obtain a baseband signal, and demodulates the baseband signal to obtain a bit steam. As shown in FIG. 2, in the multi-fixed-gain-branch receiver which switches before demodulation, the digital receiving path module is divided by the multi-branch synchronous switching module into two parts, i.e. the M digital receiving path fore-stages and the digital receiving path post-stage. The M digital receiving path fore-stages perform partial processing on the signals from the ADCs, the multi-branch synchronous switching module switches synchronously under the control of a demodulation synchronization signal to select and output a branch signal having appropriate power, and the outputted signal is further subjected to digital processing, such as demodulation by the digital receiving path post-stage to output a resulting bit stream. It is noted that the position where the multi-branch synchronous switching module is interposed into the digital receiving path module is dependent upon actual design of the receiver, and is not limited strictly, as long as it is deployed before the demodulation processing.
The input signal received by the multi-fixed-gain-branch receiver which switches before demodulation is subjected to processing, such as frequency mixing, filtering, and amplification by the upstream analog receiving path module, inputted to the M fixed-gain branches, which changes the power of the signal, respectively, and then subjected to processing, such as filtering and decimation by the M ADCs, respectively, to obtain digital signals. The obtained digital signals pass through the M digital receiving path fore-stages, the multi-branch synchronous switching module selects a branch having a signal with appropriate power, and the signal is demodulated by the digital receiving path post-stage to output the bit stream.
In addition, similar to the single variable-gain branch receiver, the input signal of the multi-fixed-gain-branch receiver which switches before demodulation is an analog band-pass signal. If the upstream analog receiving path module and the fixed-gain branch module include analog I&Q demodulating components, the fixed-gain branch module outputs analog baseband signals, i.e. two analog low-pass signals of I and Q; otherwise, the fixed-gain branch module outputs an analog band-pass signal. Correspondingly, the ADC may include a single-path ADC or I&Q ADCs.
Further, a single bit stream is outputted from each of the digital receiving paths if the multi-fixed-gain-branch receiver which switches before demodulation is a single-carrier receiver, and multiple bit streams are outputted, if the multi-fixed-gain-branch receiver which switches before demodulation is a multi-carrier receiver.
The multi-fixed-gain-branch receiver which switches before demodulation is disadvantageous in the following aspects.
(1) The switching performed before demodulation needs to be synchronous. In other words, the switching is performed only at synchronous boundaries of the received signal, and therefore not only the circuitry complexity is increased, but also the channel change cannot be traced in real time by the switching.
(2) The input signal is inputted into multiple branches simultaneously, due to different circuitry characteristics of various branches, phases or amplitudes of the various branch signals at the same point of time before the switching may be different from each other. Further, switching time granularity is restricted to be lager than the duration of the signal because the receiver demodulates simultaneously the signal within the entire duration of the signal. If a large change on the input signal occurs within the duration of the input signal and exceeds the non-simultaneous dynamic range of the single path, the signal outputted cannot be normal within the entire duration of the signal and is inevitably saturated or lower than the sensitivity, regardless of the switching by the multi-branch synchronous switching module, as a result, demodulation performance within the duration of the signal is affected.
FIG. 3 is a diagram showing the basic structure of a multi-fixed-gain-branch receiver which switches after demodulation. As shown in FIG. 3, the multi-fixed-gain-branch receiver which switches after demodulation is similar to multi-fixed-gain-branch receiver which switches before demodulation. The digital receiving path module in the multi-fixed-gain-branch receiver which switches after demodulation is not divided into two parts by a multi-branch synchronous switching module, and after signals are demodulated completely, the multi-branch synchronous switching module selects and outputs a branch signal having the best demodulation performance. Because a synchronous signal can be obtained directly from the demodulated signals, no specific demodulation synchronization signal is required to control the switching for the switching branch after demodulation.
Additionally, it should be noted that, it is possible that no upstream analog receiving path module is included in the receiver in practice. In other words, the input signal of the receiver is inputted into the fixed-gain branch module. Further, analog I&Q demodulating components may be included in various fixed-gain branch modules, instead of the upstream analog receiving path module. Alternatively, neither the upstream analog receiving path module nor the various fixed-gain branch modules include the analog I&Q demodulating components, and digital I&Q signals are obtained from a single sampled digital band-pass signal by a digital component using a digital approach.
The technology of the multi-fixed-gain-branch receiver which switches after demodulation is disadvantageous in the following aspects.
(1) The demodulation is performed before the switching, and therefore M digital receiving path modules each including a demodulating component is required for the receiver, leading to a resource waste.
(2) Similar to the technology of the multi-fixed-gain-branch receiver which switches before demodulation, in the technology of the multi-fixed-gain-branch receiver which switches after demodulation, demodulation performance is also lowered in the case where a large change of the signal occurs within duration of the signal.
Accordingly, such a receiver and a wireless signal receiving method, in which switching between branches may be performed without control of a specific synchronous signal, a signal change may be traced rapidly, and demodulation performance may be ensured in the case where a large change of a signal occurs within duration of the signal, are not provided in the prior art.